Dial digit information, representative of the numbers of a called telephone station, is presently sent from a telephone by one of two commercially accepted methods. The oldest type employs a standard rotary dial and ancillary apparatus. In the standard rotary type dial systems, digit information is sent as a set of pulses generated by having the dial pulsing contacts interrupt the telephone line a number of times equal to the number of the dialed digit. The second is the touch and tone type dial and ancillary apparatus. In the touch type system, the digit information is sent as a parallel combination of selected audio frequency signals assigned to the number of the dialed digit actuated by depressing the push button associated with the number of the digit dialed. The touch type dial consists of a selector pad having a series of ten push buttons arranged in rows and columns with each push button representative of a particular number of from one to ten (zero). A multi-frequency signal generator is associated with the push-buttons to produce a characteristic audio signal or tone for each of the numbers.
The central telephone exchange must have the necessary equipment for deciphering these two types of signals. Unfortunately, many existing telephone exchanges do not possess the equipment for deciphering tone type dialing information signals and decipher only rotary dial type signals. Hence, telephone users in those telephone exchange areas not having the tone type deciphering equipment who wish to use a touch type dial for ease and convenience, must use a presently existing device known as a touch-to-rotary converter. Devices of this type respond to the operation of a touch type switch operated by the telephone user but send a series of pulses like the rotary dial instead of the multifrequency tones.
One existing touch-to-rotary converter is specified in an application note of the General Instrument Company, Hicksville, New York. The application note describes a storage and pulsing circuit using an integrated circuit, Model No. AY5- 9100. This stores binary input information sequentially applied to its input and sends series of pulses representative of the binary information. The note specifies the ancillary component apparatus necessary to manufacture a touch-to-rotary converter. As previously described in part, the touch type selector pad or dial, as variously termed, has ten push buttons arranged in rows and columns, more particularly, in four rows and three columns. Four "row" switches and three "column" switches are associated with the push buttons. These switches are typically of a leaf-spring construction. Each individual push button, when depressed, actuates a corresponding one of the row switches and one of the column switches and the common switch. As presented in the cited application note, the storage and pulsing circuit of the integrated circuit, No. AY5-9100, has a "strobe" input and requires a synchronizing or strobe input signal to actuate the memory within the integrated circuit so that the circuit accepts the binary code information of the dialed digit as presented at an input. For this purpose the application note specifies that the common switch associated with the touch type dial pad be coupled to the strobe input. In such a structure, misalignment due to assembly tolerances or metal fatigue of the leaf-spring switches on the touch type selector pad may cause misdialing. For example, if a selected push button is depressed and the common switch closes prior to or coincident with the associated row or column switches, the storage and pulsing circuit may record in its memory erroneous information.